The invention relates, generally, to new and improved methods and apparatus using mechanical separation between the drilling fluid and the displacement fluids, and specifically, to the use of swab cups to mechanically separate the drilling fluid from the displacement fluids, in combination with a casing scraper to remove debris from the inner wall of the casing or other tubular members. The method and apparatus can also be used to clean up downhole fluids, and can be used to wipe well casing and completion risers clean, even with varying internal diameters.
It is well known in the art of the completion and/or the workover of oil and gas wells to displace the drilling fluid with a completion fluid or a workover fluid. A workover fluid will typically be either a surface cleaning fluid, such as an acid, to clean out the perforations in the casing, or a formation treating chemical which can be used with proppants to prop open the formation. The completion fluid will typically be a clear, heavy brine such as calcium chloride, calcium bromide or zinc bromide, or various combinations of such heavy brines. The density of such clear brines is generally selected and controlled to ensure that the hydrostatic head or pressure of the fluid in the wellbore will match the hydrostatic pressure of the column of drilling fluid being displaced.
Displacement xe2x80x9cspacersxe2x80x9d, as they are commonly named, are used between the drilling fluid and the completion fluid, and these are typically formulated from specific chemicals designed for the specific base drilling fluid being displaced, and will typically include weighted or unweighted barrier spacers, viscous barrier spacers, flocculating spacers, and casing cleaning chemicals, as desired.
It is well known in this art that complete displacement of the drilling fluids is critical to the success of completion and/or workover operations. It is extremely important that the brines not be mixed with the drilling fluid itself.
In the prior art, there are two principal displacement methods, viz., direct and indirect. The choice between direct and indirect has depended upon casing-tubing strengths, cement bond log results, and exposure of the formation of interest. If the cement bond logs and the casing strength data indicate that the casing would withstand a calculated pressure differential, ie., that the casing would not rupture, and that the formation of interest is not exposed, the conventional technique has been that of indirect displacement.
In a typical indirect displacement, large volumes of sea water are used to flush the drilling fluid out of the well. When applying the flushing method, however, it is very important that the pressure of the salt water flush not exceed the pressure which would burst the casing being flushed.
Direct displacement of the drilling fluid, used by those in this art whenever there are pressure problems or the formation of interest is exposed, uses chemical agents and weighted fluids to clean the wellbore and to separate the drilling fluid from the workover/completion fluid. Because a constant hydrostatic pressure is maintained, pressure problems are eliminated. Direct displacement is normally used when (1) casing and tubulars cannot withstand the pressures associated with the indirect displacement procedure; (2) when the formation of interest is exposed; (3) if a source of flushing water, typically salt water, is not readily available; or (4) in the event of disposal and discharge restraints being imposed on the particular well or group of wells.
A common element to both the direct and indirect displacement procedures is the use of barriers and cleaning chemicals (xe2x80x9cspacersxe2x80x9d) for effective hole cleaning and separation between the drilling fluid and the completion/workover fluid. The primary purpose of a barrier spacer is to provide a complete separation between the drilling fluid and the completion/workover fluid. In such prior art systems, the spacer fluid must be compatible with both the drilling fluid and the workover/completion fluid.
However, to the best of applicant""s knowledge, the prior art has not had the ability to displace the drilling fluid with a workover/completion fluid without using a spacer fluid between the drilling fluid and the workover/completion fluid.
It is also well known in this art to use casing scrapers to clean-off the interior wall of a downhole casing, but typically, cannot use the same tool in cleaning casing strings or other tubular members of varying diameters. The following prior art United States patents show various combinations of casing scrapers and/or swab cups, but none of such patents, taken alone or in combination, show or suggest the combination of the present invention.
Gibson 2,362,198: This shows a casing scraper (brush) in combination with swab cups 17 in FIG. 1, and the flow of various fluids (water, circulation fluid or cement) through the hollow rod 10. This device is meant to vertically reciprocate to clean the interior of casing, but does not suggest using the swab cups as a mechanical separation of the drilling fluid and the completion fluid.
Hodges 2,652,120: This shows a casing scraper 22 and a seal ring 23 (an inflatable packer instead of a swab cup) and a reciprocating rod 15 to create a suction which cleans out the perforations 12 in the casing (see Col. 3, lines 48-68 concerning its operation). The patent does not suggest the concept of mechanical separation of the fluids.
Hodges 2,687,774: This is related to Hodges 2,652,120, discussed above, and is of no additional relevance.
Keltner 2,825,411: This shows a swabbing device which includes a typical chemical cleaning process in conjunction with the reciprocating swabbing process. (See Col. 6, lines 1-11 for the chemical cleaning process.) There is no suggestion of mechanically separating the completion fluid from the drilling fluid.
Maly, et al., 3,637,010: This is of very little, if any, relevance, showing packers 66 and 68 (see FIG. 2) in a gravel packing operation in horizontal wells.
Jenkins 4,838,354: This shows a casing scraper with blades 18 and a packer 76 supported by a tubing string 12 having a drill bit 48 at its lower end, all within the casing 68. The production packer 76 is apparently anchored to the casing wall independently of the downward movement of the tubing string 12. This patent does not suggest the concept involving the mechanical separation of the fluids. In fact, as the pumped fluid exits the drill bit, the fluid returns back through the annulus 82 between the tubing string 12 and the inner tubular member 66 passing through the interior of the packer 76.
Stafford 4,892,145: This shows chevron packings 22 and 23, on opposite sides of a cavity xe2x80x9cACxe2x80x9d (see FIG. 2). Knife blade 34 functions as a scraper between the chevron packings 22 and 23. Once the chevron packings have isolated the perforations in the casing, fluid is pumped out of openings 27 in the mandrel 11 to clean out the perforations.
Caskey 4,921,046: This shows a cleanup tool for cleaning the interior of a casing string having a packer cup 18 for sealing the tool to the casing wall, and
which pumps clean out fluid out through the port 84 into the casing below the packer cup. The debris is then picked up by the pumped fluid and pumped into the lower end of the mandrel 70 and pumped back to the earth""s surface. This does not suggest a mechanical separation of the completion fluid and the drilling fluid.
Jenkins 5,076,365: This is the same disclosure as 4,838,354, discussed above, and the same comments apply.
Ferguson et al. 5,119,874: This well clean out system is used to pump sand and other debris out of the bottom of a producing well, but aside from using swab cups, has essentially no relevance to the present invention.
It is therefore the primary object of the present invention to provide new and improved methods and apparatus for displacing the drilling fluid in a wellbore with one or more completion and/or workover fluids.
It is yet another object of the present invention to provide a new and improved cleaning and/or wiping of the interior of drilling and completion risers.
It is another object of the present invention to provide new and improved separation of the drilling fluid from one or more completion and/or workover fluids.
It is another object of the invention to provide new and improved methods and apparatus for cleaning the interior surfaces of casing strings or other tubular members having progressively smaller internal diameters as a function of depth of the casing in earth boreholes.
The present invention is directed, generally, to methods and apparatus which employ a plurality of swab cups integrally located within a string of tubular pipe, positioned within a cased earth borehole, or within a drilling or completion riser, and having drilling fluid located on one side of the plurality of swab cups and the workover fluid or the completion fluid located on the other side of the plurality of swab cups, resulting in a mechanical separation of the drilling fluid and the workover/completion fluid.
In one mode of the invention, the tubular is lowered into the cased wellbore, typically loaded with drilling fluid, with the completion/workover fluid being pumped behind the plurality of swab cups. This action forces the drilling fluid to be pumped from the wellbore through the interior of the tubular back near or to the earth""s surface.
As an additional feature of the invention, a mechanical scraper is run below the swab cups to help clean the interior of the well casing and to prevent or lessen any damage to the swab cups.
In an alternative embodiment of the invention, the displacement fluid is located between a pair of swab cups and the drilling fluid located in the borehole annulus other than between the pair of swab cups.
Alternatively, the combination swab cup and scraper assembly is run to the desired depth in the cased wellbore, or riser, and then pulled out of the hole, bringing the drilling fluid or other fluid to be displaced towards the earth""s surface by taking returns up the annulus, with that portion of the cased borehole, or the riser, below the assembly being back-filled with the displacement fluid.
As a special feature of the invention, the tool includes swab cups of varying external diameters, in which at least one or more of them are sheared upon meeting decreased diameter tubulars, allowing the tool to be used in varying diameter tubulars.